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He’s big, green and fat as a finger, with an alarming spike on his rear end. And he has weird orange “eyes” that seem to stare at you.

At first glance, the tomato hornworm looks like something out of a horror movie. So creepy, so unsettling somehow. Most of us recoil in shock when encountering one for the first time.

Then we think nervously: “How disgusting. Better kill it.”

But please, folks, resist the urge. I’ve actually become quite fond of this freakish little fellow which — at 10 centimetres long — is the largest garden caterpillar we are likely to come across in Ontario. He often shows up unexpectedly on my tomato plants at this time of year– and it’s always a surprise.

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A welcome one, too. Nowadays, my impulse is no longer to play executioner with a brick or a bucket of soapy water. Instead, I leave Manduca quinquemaculata (to use his tongue-twisting Latin name) to meander around in my tomato plants as he pleases, happily chomping away. Then, satiated, I know he will vanish from the veggie plot as quietly and mysteriously as he came.

Why play Lady Bountiful? Several reasons.

First, unlike some gardeners who experience serious infestations of these caterpillars, I’ve never once had more than half a dozen hornworms appear in my garden. Second, they always do this late in the season, and they mostly strip the leaves off the tops of tomato plants that have finished growing, A few sometimes also nibble holes in the tomatoes themselves, but this doesn’t happen regularly.

Thus, since they aren’t really making a dent in my eagerly-awaited crop, I don’t see any point in killing them.

Yet here’s the most important reason to let the homely hornworm live to see another day: he’s a valuable garden helper on two counts.

If his back is covered with a row of little white eggs, (I’ve personally never seen this), it means he’s playing host to a beneficial tiny insect called the braconid wasp.

But if these joy riders don’t get to eat his innards while he’s still alive (yes, that’s what braconid wasps do; Mother Nature isn’t as benign as we like to think) the hornworm will metamorphose into something far more aesthetically pleasing — a hummingbird moth.

This magnificent moth is so big, with a wing span of 10 to 25 centimetres across, it truly does resemble a hummingbird. Its colouring is grey and sort of pink, or brown and gold. But like all moths, it’s a creature of the night. I’ve only ever noticed solitary specimens in my garden at dusk. They hover, helicopter-like, over my tall wild tobacco (NIcotiana sylvestris) plants, before poking deep into the trumpet-shaped blooms to suck out the nectar — an awe-inspiring sight, which is unfortunately rare.

Experts in fact say hummingbird (or hawk) moths make great garden pollinators – another point in their favour. But we aren’t likely to see them moving from flower to flower during the daylight hours.

That leaves those much-hated hornworms. They definitely ARE viewable. So, here’s my plea: even though the internet is awash with pest control tips, think twice. If these caterpillars are doing a number on your tomatoes, try moving them on to something else in the huge Solanaceae family of plants. That’s where they like to dine. You can find many options, including potatoes, pepper plants and wild deadly nightshade.

If possible, though, leave them be, because tomato hornworms can be fascinating. They’re often so perfectly camouflaged among tomato leaves, you need eagle eyes to spot them. But once you’ve located one, grab a seat, sit down and listen.

If your place is quiet enough, you can actually hear this bizarre garden visitor chomping on his dinner.

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